New Catalina 25 Sailer - Need some help with basic marine plumbing

[rcoleman67]

I've been a bass fisherman all my life running 21 foot fiberglass hulls, 200 HP outboards, 110lb thrust trolling motors,
electronics, basic DC wiring, bilge pumps, live well pumps, etc. but I'm struggling to get my head around all the sailboat and sailing knowledge.

Currently I'm needing to replace my pvc plumbing lines (they've never been replaced and are really, really gross) in the galley sink, ice box, head, etc. I'm attaching a "crude" diagram showing my plumbing lines running from the galley sink and the ice box to the thru hull. There's a "T" connector with the galley sink attached on one side and the ice box drain hose on the other side. The drain from the galley sinks takes a 90 degree/sharp turn to miss the top of the highest draw under the sink, winds its' way behind the ice box and then has to come up 3-4 inches to the thru hull. The drain from the ice box slopes down and runs along the hull past the thru hull and then makes a bow and comes up 3-4 inches to the other side of the thru hull. I don't understand how water would easily drain via gravity down and then back up thru the thru hull. What keeps water from backing up thru an open thru hull into the lines?

Can someone please explain how this works or point me to a good resource. I can't stand not knowing how stuff works. Also, when should my thru hulls be open and when should they be closed?

Thanks in advance for sharing and helping me get squared away. I love working on my boat and my family and I are loving learning to sail. Whoever said you can't teach an old dog new tricks sure didn't know me! God Bless guys for help a "moroon" like myself <grin> ...

 

[Ralph Johnstone]

The easiest way to look at this is that "water runs downhill."
It doesn't matter what happens during the journey, as long as the waste water level inside the boat, is higher than the water line on your hull.

The waste water level is the final resting level of the waste water :

- in the sink, it's a few inches below the bottom of the sink.
- in the cooler, it's a few inches below the bottom of the floor of the cooler.

The hose DOES NOT DRAIN DRY.

 

[dlochner]

You're right, water doesn't run up hill. I'm assuming that Catalina understood this and some prior owner didn't or he believed the drains needed a water trap because the drains in his house need them.

Boat drains don't need water traps, except for the ice box drain in some installations. Ice Box drains may have a dip to block leakage of cold air from the ice box. In those cases the ice boxes often have a pump to pull the water out of the ice box. Other wise the drains should flow downhill.

Most OEM plumbing is hose and not solid PVC, except for the sink drain tailpieces. Look at possible hose routings that would allow for continuous downward slope.

 

[Richard19068]

What keeps water from backing up thru an open thru hull into the lines?

Nothing. The water level in the hose will rise to boat's waterline.

Also, when should my thru hulls be open and when should they be closed?

Most prople suggest keeping thru hull valves closed when you are not aboard. It kind of depends on how you feel about the integrity of the hose and its attachment to the valve.


I agree with dlochner that the hoses should have a continuous downward slope. No sense in having a trap for junk to get stuck in.

 

[Stu Jackson]

You should get to know these skippers, too:

Association Forum - Catalina 25 Specific Forum